About the SAP 4.3

Published May 2008, the Synthesis and Assessment Product 4.3 (SAP 4.3): The Effects of Climate Change on Agriculture, Land Resources, Water Resources, and Biodiversity in the United States is the most extensive examination of the impacts of climate change on important U.S. ecosystems undertaken to date. SAP 4.3 is one of a series of 21 Synthesis and Assessment Products being produced under the auspices of the U.S. Climate Change Science Program (CCSP), which coordinates the climate change research activities of U.S. government agencies. [all documents]

This assessment is based on extensive review of the relevant scientific literature and measurements and data collected and published by U.S. government agencies. Written by a team of 38 – scientists and researchers from universities, national laboratories, non-government organizations, and government agencies – the authors are experts in the fields of agriculture, biodiversity, and land and water resources. To generate this assessment of the effects of climate and climate change, the authors conducted an exhaustive review, analysis, and synthesis of the scientific literature, considering more than 1,000 separate publications.

The U.S. Department of Agriculture (USDA) is the lead agency for this report, with the National Center for Atmospheric Research (NCAR) managing the effort under a cooperative agreement with USDA. The SAP 4.3 work was overseen by the Committee for the Expert Review of SAP 4.3, a federal advisory committee reporting to the USDA.

Major Findings

Climate change is already affecting U.S. water resources, agriculture, land resources, and biodiversity, and will continue to do so.

Grain and oilseed crops will mature more rapidly, but increasing temperatures will increase the risk of crop failures, particularly if precipitation decreases or becomes more variable.

Higher temperatures will negatively affect livestock. Warmer winters will reduce mortality but this will be more than offset by greater mortality in hotter summers. Hotter temperatures will also result in reduced productivity of livestock and dairy animals.

Forests in the interior West, the Southwest, and Alaska are already being affected by climate change with increases in the size and frequency of forest fires, insect outbreaks and tree mortality. These changes are expected to continue.

Much of the United States has experienced higher precipitation and streamflow, with decreased drought severity and duration, over the 20th century. The West and Southwest, however, are notable exceptions, and increased drought conditions have occurred in these regions.

Weeds grow more rapidly under elevated atmospheric CO2. Under projections reported in the assessment, weeds migrate northward and are less sensitive to herbicide applications.

There is a trend toward reduced mountain snowpack and earlier spring snowmelt runoff in the Western United States.

Horticultural crops (such as tomato, onion, and fruit) are more sensitive to climate change than grains and oilseed crops.

Young forests on fertile soils will achieve higher productivity from elevated atmospheric CO2 concentrations. Nitrogen deposition and warmer temperatures will increase productivity in other types of forests where water is available.

Invasion by exotic grass species into arid lands will result from climate change, causing an increase fire frequency. Rivers and riparian systems in arid lands will be negatively impacted.

A continuation of the trend toward increased water use efficiency could help mitigate the impacts of climate change on water resources.

The growing season has increased by 10 to 14 days over the last 19 years across the temperate latitudes. Species’ distributions have also shifted.

The rapid rates of warming in the Arctic observed in recent decades, and projected for at least the next century, are dramatically reducing the snow and ice covers that provide denning and foraging habitat for polar bears.

The National Center for Atmospheric Research (NCAR) is a federally funded research and development center devoted to service, research and education in the atmospheric and related sciences. Our primary sponsor is the National Science Foundation (NSF), with significant additional support provided by other U.S. government agencies, other national governments and the private sector. NCAR's mission is to understand the behavior of the atmosphere and related physical, biological and social systems; to support, enhance and extend the capabilities of the university community and the broader scientific community – nationally and internationally; and to foster the transfer of knowledge and technology for the betterment of life on Earth. NCAR is managed by the University Corporation for Atmospheric Science under a cooperative agreement with NSF.

U.S. Climate Change Synthesis Program

CCSP SAP4.3 is a collaborative effort led by the US. Department of Agriculture (USDA) with assistance from supporting agencies.